This invention relates to removing contaminants from a waste fluid, and more particularly to an apparatus and method utilizing a source of hydroxyl radicals and ultraviolet (UV) radiation to remove contaminants.
Purifying apparatus and methods for removing organic and inorganic contaminants and microorganisms from various fluids such as water are known. Exemplary methods include incineration, chemical detoxification, ozonation and exposure to ultraviolet (UV) radiation. These methods, however, generally have not attained wide acceptance either on a large or small scale because of expense, size of the equipment needed, formation of undesirable by-products (e.g., toxic off-gases), and other similar problems.
An alternative is to utilize ozonation in combination with exposure to radiation such as UV radiation. The UV radiation is used to kill microorganisms and viruses, and is used as a catalyst for the ozonation reaction. This reaction is generally: EQU O.sub.3 +H.sub.2 O+h.nu..fwdarw.H.sub.2 O.sub.2 ( 1) EQU H.sub.2 O.sub.2 +h.nu..fwdarw.20H (2) EQU H.sub.2 O.sub.2 .revreaction.HO.sub.2.sup.- +H.sup.+ ( 3) EQU HO.sub.2.sup.- +O.sub.3 .fwdarw.O.sub.3.sup.-.+HO.sub.2. (4) EQU HO.sub.2..revreaction.H.sup.+ +O.sub.2.sup.-. (5) EQU O.sub.3 +O.sub.2.sup.-..fwdarw.O.sub.2 .sup.+ O.sub.3.sup.-.(6) EQU O.sub.3.sup.-.+H.sup.+ .fwdarw.OH.+O.sub.2 ( 7)
Reactions (3)-(7) demonstrate how ozone can be utilized to generate hydroxyl radicals. The hydroxyl radicals (HO--) are then used to react with contaminants, e.g., organic contaminants, as follows: EQU HO.+organic contaminants .fwdarw.CO.sub.2 +H.sub.2 O+O.sub.2( 8)
The use of ozonation (or other methods using hydroxyl radicals) and UV radiation, however, has been limited from a commercial standpoint for use in comparatively small units or installations away from domestic water supplies. Thus there has been considerable interest in improving ozonation and UV treatment techniques.
For example, U.S. Pat. No. 4,230,571 to Dadd proposes a method wherein UV radiation generates ozone from air, the ozone is mixed with the water to be purified and the water/ozone mixture is subjected to UV radiation. The water/ozone mixture is directed through a helical path around the UV radiation source to extend the duration of exposure. U.S. Pat. Nos. 4,273,660 and 4,274,970 to Beitzel propose methods using a UV lamp positioned around a transparent tube for carrying the water. Water within the transparent tube is moved turbulently. U.S. Pat. No. 4,752,401 to Bodenstein proposes a method and apparatus for treating water wherein the water flows in direct contact with an ozone-producing UV lamp.
There has also been interest in improving the various components needed for the ozonation and UV treatment techniques, namely the means for ozonating the water, the UV lamp itself, the chamber wherein the UV and the water are reacted, and the like. For example, U.S. Pat. No. 5,120,450 to Stanley, Jr. proposes a reaction vessel wherein an interior surface thereof comprises a plurality of ridges covered by a non-stick material. The ridges are said to stabilize placement of the non-stick material. U.S. Pat. No. 4,948,980 to Wedekamp proposes a tubular UV radiation device having at least two UV light sources with oblong flat in cross-section reflectors external to the tubular body. See also, for example, U.S. Pat. Nos. 3,634,025 and 3,700,406 to Landry and 4,101,777 to Reid.
It would be highly desirable to provide a method and apparatus for removing contaminants from a waste fluid stream efficiently and effectively, and that can be used on a large or small scale.